Graphite producer and battery anode material developer Volt Resources Limited (ASX: VRC) has unveiled successful LIB cell cycle testing results using coated spheronised purified graphite (CSPG) produced from natural graphite originated at Bunyu Resource in Tanzania.
Managing Director, Trevor Matthews, said the results show very low irreversible capacity loss after 100 cycles and the continuation of low capacity loss after 170 cycles.
Low capacity losses relate to battery life and this measure is a key performance indicator for battery anode material to be used in the production of lithium-ion battery technologies.
The testwork programme was undertaken by an established commercial graphite producer and processor, American Energy Technologies Co. (AETC) which is headquartered in Illinois, USA.
We continue to be delighted with the battery cycle testwork results reported by AETC,” Mr Matthews said.
“This has confirmed Bunyu’s flake graphite is suitable for use in the production of battery-ready anode material for energy storage solutions.
“Now that we have completed 170 cycles of the battery cell testwork programme with Bunyu flake, we will shortly commence feasibility studies for the development of battery anode production facilities in Europe and the USA.
“Additionally, we will undertake an evaluation and sampling programme with a number of technology and battery end-user groups which we have engaged with in the past months, to further our commercialisation objectives in the electric vehicle, consumer and energy storage battery platforms in Europe, the United States and Asia.
“lt will be adopting the inverted flow sheet for its downstream operations following the successful spheronisation and purification results achieved during the testwork programme.
“The use of this flowsheet will allow us to not only convert a significant portion of our graphite into battery ready anode material for lithium-ion batteries, but will also generate a range of ultra-high purity by-products for use as electrically conductive diluents in battery cathodes and in a variety of valuable non-battery applications.”
Battery Cell Cycling Testwork
The testwork program’s goal is to develop a technical support data package for market introduction of the Bunyu natural graphite product and the provision of battery ready CSPG material for samples to be provided to potential LIB manufacturing customers.
The programme involved the production of SPG, followed by its surface coating prior to commencing extended cycling in batteries. Cycling tests assess the initial electrochemical performance of carbon coated spherodised graphite in the industry standard CR2016 coin cells (i.e. reversible, irreversible capacity and irreversible capacity loss).
The programme is designed to perform longterm cycling (100 cycles initially), which is used to assess the viability of the Bunyu CSPG for energy storage applications.
Initial electrochemical performance of Bunyu Graphite is presented in the chart 1 below. This graph represents a galvanostatic charge-discharge curve commonly used in the industry to derive values of reversible and irreversible capacity, as well as first cycle efficiency. It is evident that Bunyu graphite has a reversible capacity on the order of 355 mAh1/g, with irreversible capacity loss amounting to less than ten percent (i.e. 8.04%)
Long-term Cycling Results
Three cells containing Bunyu CSPG are being used for the long-term cycling testwork. The results from the three cells cycling performance are shown below and are consistent with LIB battery-grade material’s specifications.
Mr Matthews said it is worth noting that cells designed for long term cycling are intentionally built for slightly lower capacity ratings, therefore the reversible capacity values for the three cells in the test series range between 315 and 320 mAh/g.
These cells demonstrate highly consistent performance with virtually negligible degradation from cycle to cycle. The flat curve signals that Bunyu graphite could compete not only with other natural graphite battery anode material (BAM), but also a great number of costlier synthetic graphite BAM offerings, in its long-term cycling performance.
The Cell Comparison Maximums show excellent cell-to-cell stability and extremely low 1.79% reversible capacity decay (or 98.21% capacity retention) after 100 cycles. Further results were a low 2.69% reversible capacity decay (or 97.31% capacity retention) after 150 cycles and 2.83% reversible capacity decay (or 97.17% capacity retention) after 170 cycles.